The art has provided a number of different swimming pool covers, but, generally speaking, these covers can be divided into two major categories. The first category is that of Summer covers, and the second category is that of Winter covers. Summer covers are, generally, used to cover the surface of the pool during the swimming season, so as to conserve the heat of the water in the pool, especially during the cooler Spring and Fall swimming days. These covers are, generally speaking, made of "bubble" plastic film, such that there are cells of air sealed between two films of plastic, and those cells provide sufficient buoyancy that the cover will float on the surface of the water in the pool. During cooler days, especially, in the Spring and Fall, sunlight will pass through those Summer covers and be absorbed by the water in the pool, thus heating the pool. Summer covers also prevent heat loss from the surface of the water during cool evenings and nights, especially in the Spring and Fall, and thus conserve the heat of the water in the pool. For this latter reason, these Summer covers are often referred to as "pool blankets."
Such Summer covers are, therefore, impervious to water, and during periods of rain, water may collect on Summer covers. However, since those Summer covers are not attached to the sides of the pool in any substantial way, water collected on the Summer covers simply spills over the edges of the covers into the pool, and thus Summer covers remain in a condition such that they will float on the surface of the water in the pool.
However, any silt or debris which accumulates on Summer covers will also spill off of the Summer cover and into the pool. This is not normally a difficulty, since during the swimming season, the pool must be routinely cleaned, and such silt and debris are removed during that cleaning.
The second category of pool covers, i.e. Winter covers, are intended for covering the pool during periods of non-use, i.e. from the Fall and into the following Spring. These covers serve very different purposes from Summer covers, and the functions, characteristics and uses of Winter covers are substantially different from that of Summer covers and form a very distinct cover from that of a Summer cover. A Winter cover has two primary purposes. The first purpose is that of keeping silt and debris, e.g. fallen leaves, twigs, grass cuttings, etc., from entering the pool, since, during the Winter season when the pool is not routinely cleaned, that debris can cause serious cleanliness problems in the water of the pool. The second purpose is that of preventing accidental entry into the pool by children, pets and the like. For this reason, Winter covers are often referred to as "safety" covers. While these Winter covers, in an emergency, can support the weight of a pet or child or even an adult, they are not intended to be walked upon, and that safety feature is intended only for emergency purposes, e.g. where a child may accidentally fall into the pool.
Thus, Winter covers differ from Summer covers in three main aspects. Firstly, the Winter covers must be quite sturdy in order to prevent a child or pet, for example, from accidentally falling into the pool water. Secondly, the Winter covers must be capable of substantially reducing the amount of silt and debris which can enter the pool during the Winter months. Thirdly, the Winter covers must be securely anchored to the outer portions of the pool, as opposed to Summer covers where no such anchoring is normally needed.
In the prior art, Winter covers have usually been made with a tightly-woven mesh, such as a tightly-woven olefin fiber mesh, and that mesh is disposed over the area of the pool and to at least outer portions of the pool, e.g. the coping of the pool. The mesh is very strong and is further strengthened by a series of straps which traverse the length and breadth of the mesh, providing a gridwork for further support of the cover, in the event that a child or animal falls into the pool. Those straps are anchored at the outer portions of the pool in spaced-apart anchoring positions.
During the Winter, when rain or snow falls, the mesh allows the water of the rain or snow to pass therethrough. This prevents water accumulation on the tautly secured Winter cover, and, thus, prevents the Winter cover from being weighted down and sinking beneath the surface of the water in the pool. Of course, if the cover sank beneath the surface of the water in the pool, any silt or debris that collected on the pool would mix with the water in the pool and defeat the purpose of the Winter cover. Further, the "safety" feature would be destroyed.
While these prior art Winter covers work quite well, especially in providing security for the pool and in preventing large debris from entering the water of the pool, they also suffer from a substantial disadvantage. In this regard, while the mesh of the Winter cover is relatively tightly woven in order to provide security for the pool and prevent large debris from entering the pool, the woven mesh is quite porous so as to prevent water accumulation thereon. This porous mesh allows fine debris, e.g. fine pieces of leaves, and, especially, silt, to enter the water of the pool. Over the course of the Winter, the amount of such small debris and silt can substantially degrade the quality of the water in the pool.
It would, therefore, be of considerable advantage to the art to provide a Winter cover which has the security of the prior art covers, but which at the same time prevents egress of all debris, including fine debris and silt, into the water of the pool during use of the Winter cover.